Crack Paths 2012

D W

D

^

^

Figure 5: a- Wöhler curves at final rupture, b- Wöhler curves at initiation of the rupture

The parallelism between curves on figure 5-a and figure 5-b indicates a proportional relationship between

the initiation of the rupture and the final rupture. Indeed, if we study the Basquin coefficient, we can

observe some very similar values for each temperature (Fig 6-a). The temperature does not affect the

propagation mode: initiation of the rupture appears systematically at 40%of the total life expectancy of

the tube (Fig 6-b).

100

90

80

Température

70

-30°C

20°C

120°C

(°C)

-30

20 120

60

-30°C

450

20°C

1/b

120°C

5,8

6,3

6,4

30

(fissuration)

20

6,5

6,7

10

1/b (rupture) 6,2

0

Temperature(°C)

Figure 6: a- Correlation between Basquin coefficient as a function of temperature for final rupture and

initiation of the crack, b- Proportional coefficient between the cycle number at rupture initiation and final

rupture

Initiation

crack

Figure 7: a- Localisation of the crack on the tube, b- Cross-section of the tube-header joint, c- Tube

microstructure

500